1. Field of the Invention
This invention relates to a process for forming an electrically conductive film by exposing to actinic radiation a coating that contains a nonionic electron donating compound and a halogen-substituted polymer having film-forming properties on a substrate. More particularly, the invention relates to a process for forming an electrically conductive film that contains a charge transfer complex in said halogen-substituted polymer in said coating.
2. Description of the Prior Art
The theory of the electrification of electric insulators is not fully understood, but it is known that it is a phenomenon that occurs at the interface of two insulators. As one insulator is contacted by or rubbed with another, or as the insulators are separated from each other, mechanical energy applied is converted to electrical energy in the form of static electricity. Such process of electrification is further complicated by the fact that it varies depending on the particular combination of insulators that are contacted or rubbed together.
Electrification of insulators has often presented serious problems in the industrial use of insulators. For example, it is well known that the phenomenon has fatal effects on certain sensitive materials, such as photographic photosensitive materials. The generation of static electricity on a photosensitive material can cause a static mark by the discharge of said electricity. Static marks present a very difficult problem because they cannot be detected until after the photographic material is developed. There are two main practical methods for preventing the electrification of insulators. One is to reduce the rate of static generation, and the other is to increase the rate of static dissipation. The former method either utilizes the rank of insulating materials in the triboelectric series or reduces the contact resistance of insulators. The latter method is based on increasing the electrical conductivity of the material in one way or another. In any event, the two methods are usually combined to attempt to achieve adequate control of static charges.
Most of the antistatic agents (antistats) developed to date are used in the latter method. Ion-conductive antistats are typical of these agents, and they are applied to or adsorbed on the surface of an insulator or they are incorporated in the insulator to increase its conductivity by reducing the specific resistance of the surface. Most antistats of this type comprise certain surfactants, and intrinsically they need some moisture for their effectiveness. Additionally, their effectiveness decreases rapidly during storage or under ambient conditions.
Considerable efforts have been made to develop an antistat less susceptible to temperature and moisture, particularly to moisture. One example of such efforts involves vacuum-deposition of a metal or conductive inorganic material on the surface of a polymeric film to increase its conductivity. However, not only is the conductive film thus-prepared expensive, but the conductive coating is also easily separated from the substrate by external forces. A conductive film can also be made by finely dispersing a metal or conductive carbon black into a polymer. But making the film by this method without sacrificing its physical properties involves much difficulty.
Recently, some organic charge transfer complexes have been found to have high electrical conductivity and many studies have been reported on their synthesis (e.g., G. H. Perlstein, Angew. Chem. Internat. Ed., Vol. 16, pp. 519-534 (1977) and A. F. Garito & A. J. Heeger, ACC Chem. Res., Vol. 7, p. 232 (1974)). However, it is difficult to produce a conductive film from only an organic charge transfer complex synthesized by a conventional method because the complex is generally available in a powder form which either has no film-forming properties or forms only a weak film. Therefore, the usual practice is to form a film by dispersing the complex in a polymer, but only few solvents can dissolve the complex and the resulting solution is often labile. Furthermore, if the complex is dispersed after it is ground with a ball mill, the very structure of the complex can be destroyed. For these reasons, it has been difficult to produce a uniform coating from such a complex.
U.S. Pat. No. 3,634,336 describes a method of producing a conductive film using a charge transfer complex. The electron donors illustrated in the patent are acetic acid salts of polynuclear aromatic compounds having a chalcogen as a central atom, and a desired conductive film is obtained by converting the salts to an effective charge transfer complex through anion exchange.